The present invention relates to the control of fluid flow through microfluidic conduits.
There has been a growing interest in the application of microfluidic systems to a variety of technical areas, including such diverse fields as biochemical analysis, medical diagnostics, chemical synthesis, and environmental monitoring. For example, use of microfluidic systems for the acquisition of chemical and biological information presents certain advantages. In particular, when conducted in microfluidic volumes, complicated biochemical reactions and processes may be carried out using very small volumes of fluid. In addition to minimizing sample volume, microfluidic systems increase the response time of reactions and reduce reagent consumption. Furthermore, when conducted in microfluidic volumes, a large number of complicated biochemical reactions and/or processes may be carried out in a small area, such as in a single integrated device. Examples of desirable applications for microfluidic technology include analytical chemistry; chemical and biological synthesis, DNA amplification; and screening of chemical and biological agents for activity, among others.
Traditional methods for constructing microfluidic devices have used surface micromachining techniques borrowed from the silicon fabrication industry. According to these techniques, microfluidic devices have been constructed in a planar fashion, typically covered with a glass or other cover material to enclose fluid channels. Representative devices are described, for example, in some early work by Manz, et al. (Trends in Anal. Chem. (1990) 10(5): 144-149; Advances in Chromatography (1993) 33: 1-66). These publications describe microfluidic devices constructed using photolithography to pattern channels on silicon or glass substrates, followed by application of surface etching techniques to remove material from a substrate to form channels. Thereafter, a cover plate is typically to the top of an etched substrate to enclose the channels and contain a flowing fluid.
More recently-developed methods permit microfluidic devices to be constructed from plastic, silicone or other polymeric materials. Fabrication methods include micromolding of plastics or silicone using surface-etched silicon as the mold material (see, e.g., Duffy et al., Anal. Chem. (1998) 70: 4974-4984; McCormick et al, Anal. Chem. (1997) 69: 2626-2630); injection-molding; and micromolding using a LIGA technique (see, e.g., Schomburg et al, Journal of Micromechanical Microengineering (1994) 4: 186-191), as developed at the Karolsruhe Nuclear Research Center in Germany and commercialized by MicroParts (Dortmund, Germany). LIGA and hot-embossing techniques have also been demonstrated by Jenoptik (Jena, Germany). Imprinting methods in polymethylmethacrylate (PMMA) have also been described (see, e.g., Martynova et al, Anal. Chem. (1997) 69: 4783-4789). These various techniques are typically used to fashion planar (ie., two dimensional, or 2-D) structures that require some sort of cover to enclose microfluidic channels.
Traditionally, fluid manipulation in these fluidic systems is controlled by electrokinetic and/or electrophoretic transport. These techniques involve the application of electric currents at very high voltages to control fluidic movement. Electrodes are placed within fluid channels and sufficient current and voltage is applied to cause the hydrolysis of water within the device. This hydrolysis produces a charge gradient through the channels that causes the movement of either the bulk fluid or molecules within the fluid. If sufficient electrodes and control components are provided, then such methods can be used to provide flow control within a microfluidic device. These techniques have numerous drawbacks, however, including the need for metallic electrodes within the chambers, and the connection of these electrodes to a high voltage source. Additionally, the hydrolysis of water is often accompanied by the formation of bubbles and other radicals that may have adverse effects on reactions within a microfluidic device or on the devices themselves. Accordingly, there is a need for microfluidic devices capable of providing flow control utility without requiring current and voltage to be applied directly to the fluid.
To enable complex fluid handling to be performed in microfluidic devices without applying current and voltage directly to a fluid, it is desirable to fabricate devices with integrated fluid control systems such as integrated valves and/or pumps. Generally, devices containing integrated valves or pumps are complex and difficult to manufacture. Fabrication of valve or pump structures using conventional methods can require the use of several different manufacturing techniques, thus rendering the fabrication process labor-intensive and time-consuming. This inhibits rapid development and optimization of new device designs. Additionally, tool-up costs for fabricating integrated microfluidic valve or pump structures using conventional techniques can be prohibitively high. In light of these limitations in conventional microfluidic devices, there is a clear need in the field of microfluidic devices for improved flow control devices.
In a first separate aspect of the invention, a microfluidic flow control device includes a fluidic chamber, a first and a second microfluidic channel, at least one sealing surface between the first and the second channels, and a floating element disposed within the chamber. The floating element is capable of intermittently engaging the sealing surface, and movement of the floating element affects fluid flow between the first channel and the second channel.
These and other aspects of the present invention will be apparent from the following detailed description of the preferred embodiments taken in conjunction with the figures.